PABX (Private Automatic
Branch Exchange) -
A private telephone exchange which transmits calls internally and to and
from the public telephone network.
Packet - An
arbitrary collection of data grouped and transmitted with its user
identification over a shared facility.
Packet Port -
A port on the CellPath 300 that transmits and receives packet traffic.
Packet Switching -
A communications paradigm in which packets (messages) are individually routed
between hosts with no previously established communications path.
Network - A network designed to carry data in the form of
PAD (Packet Assembler
Disassembler) - An interface device that buffers data sent
to/from character mode devices, and assembles and disassembles the packets
needed for X.25 operation.
Paired Cable -
A cable in which all of the conductors are arranged in the form of twisted
pairs. This form of cable is the one most commonly used for communications.
PAL (Phase Alternate
Line) - Largely a German/British development in the late 60s.
Used in the UK and much of Europe. Phase Alternate Line is the acronym's
expansion. The B-Y and R-Y signals are weighted to U and V, then modulated onto
a double-sideband suppressed subcarrier at 4.43MHz.
The V (R-Y) signal's phase
is turned through 180 degrees on each alternate line. This gets rid of NTSC's
hue changes with phase errors at the expense of de-saturation. The carrier
reference is sent as a burst in the back porch. The phase of the burst is
alternated every line to convey the phase switching of the V signal. The
burst's average phase is -V. (see NTSC for U.S.).
Panic Dump -
A listing of information written by the processor when it reaches a
non-recoverable condition. Contents of certain memory locations and other
program state information useful in determining the cause of the fault
condition are recorded.
Parallel Port -
An output receptacle often located on the rear of a computer. Unlike
serial, there is no EIA standard for parallel transmission, but
most equipment adheres to a quasi-standard called the Centronics Parallel
Parent Node -
The logical group node that represents the containing peer group of a specific
node at the next higher level of the hierarchy.
Parent Peer Group -
The parent peer group of a peer group is the one containing the logical group
node representing that peer group. The parent peer group of a node is the one
containing the parent node of that node.
Parity Bit -
A binary bit appended to an array of bits to make them sum all of the bits
always odd or always even.
Part 68 Requirements
(Registration) - Specifications established by the FCC as
the minimum acceptable protection which communications equipment must
provide the telephone network. Meeting these requirements does not certify
that equipment performs any task.
patch panel -
A generic device that allows for organizing and connecting the fiber optic
cables coming from the ASX-4000.
Path Constraint -
A bound on the combined value of a topology metric along a path for a specific
Path Scope -
The highest level of PNNI hierarchy used by a path.
Payload Scrambling -
A technique that eliminates certain bit patterns that may occur within an ATM
cell payload that could be misinterpreted by certain sensitive transmission
equipment as an alarm condition.
PBX (Private Branch
Exchange) - A private phone system (switch) that connects to the
public telephone network and offers in-house connectivity. To reach an outside
line, the user must dial a digit like 8 or 9.
PBX Battery -
Source of DC power for private branch exchange. Usually on the same
premises as the PBX, though PBXs are sometimes fed from the central
office over special conductors.
PC (Personal Computer)
- A computer for personal, single user use, as opposed to
other types of computers such as mainframes and minis, which are
typically shared by many users.
PCB (Printed Circuit
Board) - Flat material (fiberglass/epoxy) on which
electronic components are mounted. A PCB also provides electrical
pathways, called traces, that connect components. PCBs are very sensitive
to static electricity and must be handled with care. Also called printed
wiring board and printed circuit card.
Component Interconnect) - A local-bus standard created by Intel.
PCM (Pulse Code
Modulation) - A modulation scheme that samples the information
signals and transmits a series of coded pulses to represent the data.
PCR (Peak Cell Rate) -
Parameter defined by the ATM Forum for ATM traffic management. In CBR
transmissions, PCR determines how often data samples are sent. In ABR
transmissions, PCR determines the maximum value of the ACR.
Communications Software) - Personal Communications Software
available in ROLM, Cedar, Cypress, and Juniper makes for easy access to
external databases, rapid transfer of data files, and one-touch access to most
telephone features. Other PCS features include built-in calculator, small
phone list, reminder function, and internal clock.
PDN (Public Data
Network) - A network designed primarily for data transmission and
intended for sharing by many users from many organizations.
PDSC (Power Distribution
Servicing Cabinet) - A cabinet containing branch circuit protection
for essential AC loads.
PDU (Protocol Data
Unit) - A unit of data specified in a layer protocol and
consisting of protocol control information and layer user data.
Peak - That
part of the business day in which cellular customers expect to pay full
Peak Cell Rate -
At the PHY Layer SAP of a point-to-point VCC, the Peak Cell Rate is the inverse
of the minimum inter-arrival time T0 of the request to send an ATM-SDU.
Peak Current -
The maximum value reached by a varying current during one cycle.
Peak-to-Peak Value -
The algebraic difference between the extreme values of a varying quantity.
Peak Voltage -
Maximum voltage occurring during a cycle. For a sine wave, peak value is
1.4142 times the rms value.
Peer Entities -
Entities within the same layer.
Peer Group -
A set of logical nodes which are grouped for purposes of creating a routing
hierarchy. PTSEs are exchanged among all members of the group.
Peer Group Identifier -
A string of bits that is used to unambiguously identify a peer group.
Peer Group Leader -
A node which has been elected to perform some of the functions associated with
a logical group node.
Peer Group Level -
The number of significant bits in the peer group identifier of a particular
Peer Node -
A node that is a member of the same peer group as a given node.
Peripheral Equipment -
Equipment which itself has no on-line role but works closely with on-line
per-VC queuing -
Refers to the buffering of information on an individual virtual circuit basis.
Phase - One
of several (usually three) windings that comprise the armature. Three
phase windings have their generated voltages 120 degrees apart. Each
winding represents a Phase A, Phase B and Phase C.
Phase Hit -
Unwanted and significant shifting in phase of an analog signal, defined by
AT&T as any case where the phase of a 1004 Hz test signal shifts more
than 20 degrees. Also, error-causing events more severe than phase
jitter, especially for data transmission equipment using PSK modulation.
PHY (Physical Layer) -
The actual cards, wires, and/or fiber-optic cabling used to connect computers,
routers, and switches.
Physical Layer (PHY)
Connection - An association established by the PHY between two or
more ATM-entities. A PHY connection consists of the concatenation of PHY links
in order to provide an end-to-end transfer capability to PHY SAPs.
Physical Link -
A real link which attaches two switching systems.
A ten to the negative twelfth power farad. One millionth of a
Pigtail - A
flexible conductor attached to a component or device.
Pigtail Antenna -
The standard cellular antenna for a car. The term "pigtail" refers to the
spring-like section in the lower third of the antenna, the phasing coil.
ping (Packet Internet
Groper) - A program used to test reachability of destinations by
sending them an ICMP echo request and waiting for a reply.
Pin Jack - A small
single-contact jack used for temporary circuit connection.
Plant - A general
term to describe any telephone company equipment used to provide communications
PLCP (Physical Layer
Convergence Protocol) - A framing protocol that runs on top of
the T1 or E1 framing protocol.
Two signals are plesiochronous if their corresponding significant instants
occur at nominally the same rate, any variation in rate being constrained
within specified limits.
PLM (Physical Layer Module)
- Interface card in the CellPath 300 that provides the logic to support
the physical layer of the network link. A PLM has the actual physical port
mounted on it. Various PLMs support various physical layers, such as OC-3c/STM1
PLP (Packet Level Protocol)
- Network layer protocol in the X.25 protocol stack. Sometimes called X.25
Level 3 or X.25 Protocol.
PM (Physical Medium)
- Refers to the actual physical interfaces. Several interfaces are defined
including STS-1, STS-3c, STS-12c, STM-1, STM-4, DS1, E1, DS2, E3, DS3, E4,
FDDI-based, Fiber Channel-based, and STP. These range in speeds from 1.544Mbps
through 622.08 Mbps.
PM (Protocol Module)
- Interface card in the CellPath 300 that provides the logic supporting
the protocol layer of the network link. Various PMs support various protocols,
such as ATM cell, Frame Relay, or CBR traffic.
PMD (Physical Medium
Dependent) - A sublayer concerned with the bit transfer between two
network nodes. It deals with wave shapes, timing recovery, line coding, and
electro-optic conversions for fiber based links.
PNNI (Private Network Node
Interface or Private Network-to-Network Interface) - A protocol that
defines the interaction of private ATM switches or groups of private ATM
PNNI Routing Control Channel
- VCCs used for the exchange of PNNI routing protocol messages.
PNNI Routing Domain
- A group of topologically contiguous systems which are running one instance of
PNNI Routing Hierarchy
- The hierarchy of peer groups used for PNNI routing.
PNNI Topology State Element
- A collection of PNNI information that is flooded among all logical nodes
within a peer group.
PNNI Topology State Packet
- A type of PNNI Routing packet that is used for flooding PTSEs among logical
nodes within a peer group.
PO (Proper Operation)
- A discrete status indicator whichreports that an engine/alternator system has
transferred and is supplying AC in the central office within proper limits.
Connection - A collection of associated ATM VC or VP links, with
associated endpoint nodes, with the following properties:
1. One ATM link, called the Root Link, serves as the root in a simple tree
topology. When the Root node sends information, all of the remaining nodes on
the connection, called Leaf nodes, receive copies of the information.
2. Each of the Leaf Nodes on the connection can send information directly to
the Root Node. The Root Node cannot distinguish which Leaf is sending
information without additional (higher layer) information. (See the following
note for Phase 1.)
3. The Leaf Nodes cannot communicate directly to each other with this
connection type. Note: Phase 1 signaling does not support traffic sent from a
Leaf to the Root.
- A connection with only two endpoints.
Polarity - A
particular state either positive (+) or negative (-) with respect to some other
state, often ground.
Polling - Usually
refers to some form of data network arrangement whereby a central computer asks
each remote location in turn (and very quickly) whether they want to send some
information. The purpose is to give each user or each remote data terminal an
opportunity to transmit and receive information on a circuit or using
facilities which are being shared. Polling is typically used on a multipoint or
multidrop line. Polling is done to save money on telephone lines.
Pop - Short for
"population." One "pop" equals one person. In the cellular industry, systems
are valued financially based on the population of the market served.
Portable - A
one-piece, self-contained cellular telephone. The newest ones are so small -
weighing as little as 10 ounces - that they can be folded up and carried in a
suit pocket or purse. Portables normally have a built-in antenna and
rechargeable battery and operate with six-tenths of one watt (0.6) of power.
Positive - (1)
Describing the terminal of a storage battery from which the conventional
current leaves the battery; (2) having the ability to attract electrons; and
(3) the opposite of negative.
Pot - A
- The difference in voltages between two points.
Potential Drop -
The difference in potential, often due to a voltage drop across a resistance.
Potentiometer - A
three-terminal adjustable voltage divider.
POTS (Plain Old Telephone
Service) - The basic service of supplying standard single line
telephones, telephone lines and access to the public switched network. No added
features like Call Waiting or Call Forwarding are included in POTS.
Potting - Sealing
of components under a plastic cover to keep out moisture.
Power - The rate at
which energy (or work) is used; units include watts, horsepower, and foot
pounds per second.
Power Board or Bay -
A frame mounted power distribution panel containing switches, circuit breakers,
and fuses mounted on the face of the panel to control the standby power
equipment contained in the system. Other components, such as terminal strips,
relays, and capacitors are mounted behind the panel.
Power Circuit Breaker
- (1) A circuit breaker for use on AC circuits rated in excess of 1500V; and
(2) the primary switch used to apply and remove power from equipment.
Power Cord - A
three-wire (sometimes two-wire) cord used to make connection with an AC public
power supply (commercial power).
Power Density - (1)
Power in watts per hertz, or the total power in a band of frequencies divided
by the bandwidth in hertz; and (2) in optoelectronics, a colloquial synonym for
Power Down - The
sequence of actions necessary in order to turn off a computer or telephone
system. Not following the correct power down procedures can cause a loss of
Power Factor -
Ratio of total watts to total root-mean-square volt-amperes, i.e., the active
power to the apparent power.
Power Failure Backup
- If AC power fails, a telephone system, computer, etc. can still operate by
switching to a backup battery supply, often called a UPS (Uninterruptible Power
Power Loss - Ratio
of total power delivered to a line to the power from line into load, expressed
Power Plant - The
equipment necessary to supply processed power to a switch or other device
requiring battery backup.
Power Rack - Rack
on which such items as rectifiers, tone generators and meters are mounted in a
small central office.
Power Rated Fuse -
Fuse rated to carry a specified current indefinitely. Currents 50% greater than
the specified value will lead to the fuse blowing within five minutes.
Power Supply - That
part of switches, computers, etc. which converts the normal 120 or 240 volts AC
power to AC and DC at the various voltages and frequencies needed by various
components and circuits of the system.
Power Unit - A
component or module which provides a power supply at an appropriate voltage for
a particular item or items of equipment.
Power Up (or Power On)
- The sequence of actions necessary in order to turn a computer or telephone
Precise Dial Tone -
Mixture of 350 Hz and 440 Hz tones at -13dBm.
Primary Winding -
Transformer winding which receives an input signal from a source, thereby
creating magnetic flux in a core. This flux induces current in a secondary
Priority Loads - In
plants where load management schemes are used, a priority is assigned to each
load center. Loads with the highest priority are powered first and shed last.
Private Network - A
series of offices connected together by leased and non-leased phone lines, with
switching facilities and transmission equipment owned and operated by the user
or by the carrier and leased to the user.
Pro-Active - Taking
PROM (Programmable Read Only
Memory) - A chip that acts like non-volatile memory and is difficult
Proportional Load Sharing
- Characteristics of battery chargers in parallel that enables them to share
total load current in proportion to their output rating.
Equipment which will only work with one vendor's telephone system.
Protected AC Load -
One that must operate during prolonged loss of AC power and can tolerate an
interruption of from 0.15 to 5 seconds in the transition from commercial to
Protocol - A
specific set of rules, procedures or conventions relating to format and timing
of data transmission between two devices, typically including such things as
framing, error handling, transparency and line control. There are three basic
types of protocols: character-oriented, byte-oriented and bit-oriented.
PTT (Post Telephone &
Telegraph Administration) - PTTs, usually controlled by their
governments, provide telephone and telecommunications services in most foreign
PUC (Public Utility
Commission) - State body charged with regulating phone companies. Also
called Public Service Commission.
PWB - Printed Wire
PWR - Power.